Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
In a typical wireless communication system, a radio access network (RAN) includes one or more base stations that radiate to define one or more wireless coverage areas such as cells and cell sectors in which suitably equipped wireless communication devices (WCDs) can operate. In practice, the RAN and its served WCDs may be arranged to communicate with each other according to an agreed air interface protocol that defines a mechanism for use of communication resources to support wireless exchange of voice, data, multimedia, and/or other content. Examples of such protocols include CDMA (e.g., 1xRTT or 1xEV-DO), WiMAX, LTE, IDEN, GSM, WIFI, HSDPA, among others now known or later developed.
The air interface in each coverage area between the RAN and its served WCDs may define a forward-link (or “downlink”) for carrying communications from the RAN to the WCDs and a reverse-link (or “uplink”) for carrying communications from the WCDs to the RAN. In various implementations, these links may be defined on or more carrier frequencies or blocks of frequencies. Furthermore, on each link, various channels may be defined through techniques such as time division multiplexing, code division multiplexing, frequency division multiplexing, and the like.
By way of example, the forward-link may define a pilot channel for carrying a pilot signal usable by WCDs to detect and evaluate coverage, a paging channel for carrying page messages to particular WCDs, other overhead channels for carrying system parameter information and the like, and a number of traffic channels for carrying carry bearer traffic (e.g., call traffic) to WCDs. The reverse-link, on the other hand, may define an access channel for carrying messages from WCDs to facilitate registration, responding to pages, originating calls and the like, and a number of traffic channels for carrying bearer traffic from WCDs to the RAN. Depending on the protocol, the channel definitions may differ and other names for the channels may be used.
In practice, the reverse link access channel may define a number of containers, such as timeslots or resource elements, for carrying access channel messages from WCDs to the RAN. WCDs may then be arranged to transmit access channel messages called “access probes” in these containers. For instance, when a WCD first enters into wireless coverage and at other times, the WCD may transmit a radio access registration message in an access probe to the RAN, to notify the RAN where the WCD is located. Further, when the WCD seeks to originate a call (e.g., a voice call and/or data session), the WCD may transmit an origination message in an access probe to the RAN to trigger setup of the call. Further still, when a WCD receives a page message from the RAN on the forward link paging channel, the WCD may transmit a page response message in an access probe to the RAN. Moreover, the WCD may be arranged to transmit certain user data such as short message service (SMS) messages as data bursts in access probes to the RAN, to avoid the need to set up an air interface traffic channel for such communication.